The United States House of Representatives is poised to vote this week on a controversial national energy bill that, if passed, would deal a further setback to CNOOC's quest for Unocal.

Any decision, which would be followed almost immediately by a Senate vote, will come after a US congressional panel amended the bill to ensure that any CNOOC-Unocal deal will be subjected to a protracted 120-day review process.

Legislators want to submit the bill to President George W. Bush for approval before August 1, when congress breaks for a month. The amendment would require the US Department of Energy to conduct a four-month study on China's growing energy demands, pre-empting a separate national security review that under US law is supposed to be handled by the White House-backed Committee on Foreign Investments in the United States (CFIUS). Under the amendment, the committee could only issue its finding 21 days after the study is completed.

'This would be a time-out in the process,' said Republican Joe Barton, chairman of the House Energy and Commerce Committee. 'We're going to stop it for 120 days.'

Critics of the amendment said it was an unnecessary duplication of the CFIUS review process. In a letter to Mr Barton, Republican representative Tom Davis said the additional review 'would be a waste of taxpayer dollars and set an unfortunate precedent'.

Meanwhile, a filing by Unocal to the US Securities and Exchange Commission sheds new light on just how close the company's board of directors was to switching its support away from a rival bid by Chevron in favour of CNOOC's offer.

Unocal chief executive Charles Williamson contacted CNOOC chief executive Fu Chengyu on July 15 and 'urged him to make his best offer'.

Mr Fu called back the next day, saying he had approval from CNOOC's board to raise his offer by US$2 per share to US$69. However, Mr Fu said he would only raise the bid if Unocal agreed to pay a US$500 million breakup fee to Chevron, and to help lobby Congress in support of the bid, according to the filing.

In response, Mr Williamson 'expressed dissatisfaction' with the idea that Unocal should cover the breakup fee and said he was prevented from lobbying Congress by the contractual terms of the existing agreement with Chevron.